This invention relates to a digital signal processing device which is operable for receiving a stream of digital signals, for locating signals within the stream which are required to be modified, and for making the appropriate modifications. More particularly, but not exclusively, the invention relates to a device, suitable for use in image processing apparatus, which is operable for receiving a stream of digital signals representative of initial label values assigned to different objects within a viewed scene and for correcting the label values to take account, for example, of the perception of additional objects within the scene, or the perception that what was previously perceived to be two objects are in fact the same. The invention also relates to image processing apparatus including such a device.